The present invention relates to an improved apparatus for operating an AC elevator.
According to conventional apparatus of this type, an induction motor is used for driving a cage of the elevator, and AC power whose voltage and frequency may be varied, is supplied to the motor to operate the cage.
FIG. 1 is a diagram of an electric circuit of a conventional apparatus for operating an AC powered elevator, wherein terminals R, S and T are connected to a three-phase AC power source. A rectifier rectifies the output of the power source and a capacitor 2 smooths the DC output of the rectifier 1. An inverter 3 of the widely known PWM type is connected to the DC side of the rectifier 1 and controls the pulse width of a predetermined DC voltage to generate an AC power having a variable voltage and a variable frequency. A three-phase induction motor 4 is driven by the inverter 3. A brake wheel 5 is connected to the motor 4. A brake shoe 6 is provided oppositely to the outer periphery of the wheel 5 to provide brake force for the wheel 5 by the force of a spring (not shown). A brake coil 7 separates the shoe 6 from the wheel 5 against the force of the spring when the coil 7 is energized. A drive sheave 8 of a winch is driven by the motor 4. A main rope 9 is wound on the sheave. A cage 10 is coupled to the rope 9. A balancing weight 11 is similarly coupled. A power regenerative inverter 12 is connected between the power source at the terminals R, S and T, and the output side of the rectifier 1. The primary side of a transformer 13 is connected to the power source at the terminals R, S and T. A rectifier 14 is connected to the secondary side of the transformer 13. A start and stop device 15 is connected to the rectifier 14 and controls the starting and the stopping of the cage 10. Start and stop device 15 includes a brake controller 16 connected to and controlling the brake coil 7, a contactor controller 17, an operating electromagnetic contactor 18 which is controlled by the controller 17, and is energized when the cage 10 is started is deenergized when the cage 10 is stopped, and an operating electromagnetic contactor 19 which is similarly energized after the contactor 18 is energized and is deenergized when the contactor 18 is deenergized. Contacts 18a-18c of the electromagnetic contactor 18 are normally open. Contacts 19a-19c of the contactor 19 are also normally open. A speed controller 20 controls the inverters 3 and 12. A door controller 21 controls the opening and closing of the door of the cage provided at the cage 10.
The brake controller 16 may employ as the most simple structure the normally open contacts of the contactor 18. The contactor controller 17 may employ contacts which are closed by a start command and which are opened by a stop command, and the parallel circuit of the contacts and the contactors 18 and 19 may be connected in series with one another. Further, the door controller 21 may be constructed as shown in FIG. 2. In FIG. 2, reference character DF denotes the field coil of a door motor, and DM denotes a door motor. When contacts 51A and 51B are closed, the door motor DM is rotated toward the open side, and when the contacts 52A and 52B are closed, the motor DM is rotated toward the closed side. The door is controlled in this manner. The speed controller 20 is widely known, and speed control means may include, widely known voltage/frequency contant control, slip frequency control, vector control, etc., and the description thereof will therefore be omitted for the sake of brevity.
An apparatus for controlling a power elevator consists of the start and stop device 15, the speed controller 20, the door controller 21, etc.
The operation of the apparatus shown in FIG. 1 will be described.
The brake shoe 6 presses against the wheel 5 by the force of the spring during the stoppage of the cage 10. When a start command is dispatched to the cage 10, the contactor 18 is energized, the contacts 18a-18c are closed, and the rectifier 1 generates a DC output. The capacitor 2 is charged in this manner, and when the voltage across the capacitor 2 reaches a predetermined value, a control element (not shown) of the arms of the inverter 3 function in accordance with the operating direction thereof and generate AC power having a variable voltage and a variable frequency of the phase sequence corresponding to the operating direction. Then, the contactor 19 is energized, the contacts 19a-19c are closed, and the AC output of inverter 3 is supplied to the motor 4. Simultaneously, the brake coil 7 is energized. Accordingly, the brake shoe 6 is separated from the wheel 5. In this manner, the motor 4 starts in a direction determined by the phase sequence of the input, and the cage 10 starts running. The output frequency of the inverter 3 is regulated in accordance with a speed command signal by the operation of the speed controller 20, and the speed of the motor 4 and hence the running speed of the cage 10 is thereby controlled.
When the cage 10 is descending with a heavy load, or is ascending with an adjusted load, the difference in weight between the cage 10 and the balancing weight 11 is descending, which is called "a descending load operation". More particularly, the descending load operation means the downward operation of heavier one of the cage and the weight hung via the rope of the elevator. During this descending load operation, the motor 4 generates regenerative electric power. This regenerative electric power is sent through the inverter 3 back to the DC side, and is further sent through the inverter 12 back to the power source at the terminals R, S and T.
When the power source at the terminals R, S and T is interrupted while the cage 10 is running, the contactors 18, 19 are deenergized, and the contacts 18a-18c and 19a-19c are opened. Simultaneously, the brake coil 7 is deenergized. Accordingly, the brake shoe 6 is pressed against the wheel 5 by the force of the spring, a braking force is actuated on the wheel 5, and the case 10 is abruptly stopped. At this time the cage 10 is not likely to be in a zone where the door controller 21 is not capable of opening the door, resulting in the door being impossible to open, and passengers riding on the cage 10 are disadvantageously enclosed in the cage 10.